Does the time difference between London and São Paulo change during the year?

Yes. Because of daylight saving time the gap moves between +3h and +4h.

When is the best time to call São Paulo from London?

Between 13:00 and 17:00 in London, which is 09:00 to 13:00 in São Paulo.

London is 4h ahead of São Paulo. This gap is not fixed: daylight saving time moves it between +3h and +4h during the year.

London

United Kingdom

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São Paulo

Brazil

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A 9-to-5 day in each city overlaps for 4h. That is 13:00–17:00 in London, which is 09:00–13:00 in São Paulo.

City	Time zone	UTC offset
London · United Kingdom	Europe/London	UTC+1
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between London and São Paulo?: London is 4h ahead of São Paulo. This gap is not fixed: daylight saving time moves it between +3h and +4h during the year.
Does the time difference between London and São Paulo change during the year?: Yes. Because of daylight saving time the gap moves between +3h and +4h.
When is the best time to call São Paulo from London?: Between 13:00 and 17:00 in London, which is 09:00 to 13:00 in São Paulo.